U.S. patent application number 15/765081 was filed with the patent office on 2018-09-27 for bipolar plate, cell frame, cell stack, and redox flow battery.
The applicant listed for this patent is Sumitomo Electric Industries, Ltd.. Invention is credited to Hayato Fujita, Kiyoaki Hayashi, Takefumi Ito, Takashi Kanno, Masahiro Kuwabara, Kousuke Shiraki, Haruhisa Toyoda, Hideyuki Yamaguchi.
Application Number | 20180277858 15/765081 |
Document ID | / |
Family ID | 58666381 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180277858 |
Kind Code |
A1 |
Fujita; Hayato ; et
al. |
September 27, 2018 |
BIPOLAR PLATE, CELL FRAME, CELL STACK, AND REDOX FLOW BATTERY
Abstract
A bipolar plate for a battery has two surfaces on which a
positive electrode and a negative electrode are to be disposed
respectively. At least one of the surfaces of the bipolar plate is
provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other. The groove sections
include an introduction groove section and a discharge groove
section that are not in communication with each other. The ridge
section includes an uneven portion configured to suppress sliding
of the positive electrode or the negative electrode in a direction
in which the adjacent groove sections are arranged in parallel. The
uneven portion includes a rough surface provided on at least a part
of a surface of the ridge section and having an arithmetical mean
roughness Ra of 0.1 .mu.m to 10 .mu.m inclusive.
Inventors: |
Fujita; Hayato; (Osaka-shi,
JP) ; Kuwabara; Masahiro; (Osaka-shi, JP) ;
Kanno; Takashi; (Osaka-shi, JP) ; Toyoda;
Haruhisa; (Osaka-shi, JP) ; Yamaguchi; Hideyuki;
(Osaka-shi, JP) ; Shiraki; Kousuke; (Osaka-shi,
JP) ; Hayashi; Kiyoaki; (Osaka-shi, JP) ; Ito;
Takefumi; (Osaka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Electric Industries, Ltd. |
Osaka-shi |
|
JP |
|
|
Family ID: |
58666381 |
Appl. No.: |
15/765081 |
Filed: |
March 16, 2017 |
PCT Filed: |
March 16, 2017 |
PCT NO: |
PCT/JP2017/010813 |
371 Date: |
March 30, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/026 20130101;
H01M 8/0273 20130101; Y02E 60/50 20130101; Y02E 60/528 20130101;
H01M 8/188 20130101; H01M 8/2483 20160201; H01M 8/0258
20130101 |
International
Class: |
H01M 8/026 20060101
H01M008/026; H01M 8/0273 20060101 H01M008/0273; H01M 8/2483
20060101 H01M008/2483; H01M 8/18 20060101 H01M008/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2016 |
JP |
2016-107756 |
Claims
1. A bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed, wherein at
least one of the surfaces of the bipolar plate is provided with a
plurality of groove sections through which an electrolyte flows and
a ridge section located between the groove sections that are
adjacent to each other, the groove sections include an introduction
groove section and a discharge groove section that are not in
communication with each other, the ridge section includes an uneven
portion configured to suppress sliding of the positive electrode or
the negative electrode in a direction in which the adjacent groove
sections are arranged in parallel, the uneven portion includes a
rough surface provided on at least a part of a surface of the ridge
section, and the rough surface has a surface roughness of 0.1 .mu.m
or more and 10 .mu.m or less in terms of arithmetical mean
roughness Ra.
2. A bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed, wherein at
least one of the surfaces of the bipolar plate is provided with a
plurality of groove sections through which an electrolyte flows and
a ridge section located between the groove sections that are
adjacent to each other, the groove sections include an introduction
groove section and a discharge groove section that are not in
communication with each other, the ridge section includes an uneven
portion configured to suppress sliding of the positive electrode or
the negative electrode in a direction in which the adjacent groove
sections are arranged in parallel, the uneven portion includes a
step provided so as to have a difference in height in the direction
in which the adjacent groove sections are arranged in parallel, and
the step has a maximum difference in height of 0.1 mm or more and
0.5 mm or less.
3. A bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed, wherein at
least one of the surfaces of the bipolar plate is provided with a
plurality of groove sections through which an electrolyte flows and
a ridge section located between the groove sections that are
adjacent to each other, the groove sections include an introduction
groove section and a discharge groove section that are not in
communication with each other, the ridge section includes an uneven
portion configured to suppress sliding of the positive electrode or
the negative electrode in a direction in which the adjacent groove
sections are arranged in parallel, the uneven portion includes an
inclined surface that inclines from one groove section side toward
the other groove section side of the adjacent groove sections, and
the inclined surface has a difference in height of 0.1 mm or more
and 0.5 mm or less.
4. The bipolar plate according to claim 1, wherein the introduction
groove section and the discharge groove section satisfy any one of
(A) to (C) below: (A) the introduction groove section and the
discharge groove section each include a comb-tooth-shaped region to
form an interdigitated, opposed comb-tooth shape in which the comb
teeth are disposed to face each other in an interdigitated manner;
(B) the introduction groove section and the discharge groove
section each include a comb-tooth-shaped region to form a
non-interdigitated, opposed comb-tooth shape in which the comb
teeth are not interdigitated with each other; and (C) at least one
of the introduction groove section and the discharge groove section
is formed by a plurality of discontinuous groove sections.
5. A cell frame comprising the bipolar plate according to claim 1
and a frame body disposed on an outer periphery of the bipolar
plate.
6. A cell stack obtained by stacking the cell frame according to
claim 5, a positive electrode, a membrane, and a negative electrode
a plurality of times.
7. A redox flow battery comprising the cell stack according to
claim 6.
8. The bipolar plate according to claim 2, wherein the introduction
groove section and the discharge groove section satisfy any one of
(A) to (C) below: (A) the introduction groove section and the
discharge groove section each include a comb-tooth-shaped region to
form an interdigitated, opposed comb-tooth shape in which the comb
teeth are disposed to face each other in an interdigitated manner;
(B) the introduction groove section and the discharge groove
section each include a comb-tooth-shaped region to form a
non-interdigitated, opposed comb-tooth shape in which the comb
teeth are not interdigitated with each other; and (C) at least one
of the introduction groove section and the discharge groove section
is formed by a plurality of discontinuous groove sections.
9. A cell frame comprising the bipolar plate according to claim 2
and a frame body disposed on an outer periphery of the bipolar
plate.
10. A cell stack obtained by stacking the cell frame according to
claim 9, a positive electrode, a membrane, and a negative electrode
a plurality of times.
11. A redox flow battery comprising the cell stack according to
claim 10.
12. The bipolar plate according to claim 3, wherein the
introduction groove section and the discharge groove section
satisfy any one of (A) to (C) below: (A) the introduction groove
section and the discharge groove section each include a
comb-tooth-shaped region to form an interdigitated, opposed
comb-tooth shape in which the comb teeth are disposed to face each
other in an interdigitated manner; (B) the introduction groove
section and the discharge groove section each include a
comb-tooth-shaped region to form a non-interdigitated, opposed
comb-tooth shape in which the comb teeth are not interdigitated
with each other; and (C) at least one of the introduction groove
section and the discharge groove section is formed by a plurality
of discontinuous groove sections.
13. A cell frame comprising the bipolar plate according to claim 3
and a frame body disposed on an outer periphery of the bipolar
plate.
14. A cell stack obtained by stacking the cell frame according to
claim 13, a positive electrode, a membrane, and a negative
electrode a plurality of times.
15. A redox flow battery comprising the cell stack according to
claim 14.
Description
TECHNICAL FIELD
[0001] The present invention relates to a bipolar plate, a cell
frame, a cell stack, and a redox flow battery.
[0002] The present application claims priority from Japanese Patent
Application No. 2016-107756, filed on May 30, 2016, and the entire
contents of the Japanese patent application are incorporated herein
by reference.
BACKGROUND ART
[0003] One of known large-capacity storage batteries is a redox
flow battery (hereinafter, may be referred to as an "RF battery")
in which a battery reaction is conducted by supplying electrolytes
to electrodes. Examples of use of the RF battery include, besides
use for load leveling, use for a voltage sag compensation and an
emergency power supply, and use for smoothing the output of natural
energy, such as solar power generation and wind power
generation.
[0004] Such an RF battery typically includes, as a main component,
a battery cell including a positive electrode to which a positive
electrode electrolyte is supplied, a negative electrode to which a
negative electrode electrolyte is supplied, and a membrane disposed
between the positive electrode and the negative electrode. A
large-capacity RF battery uses a so-called cell stack formed by
stacking a plurality of battery cells and fastening the battery
cells to a certain extent. A bipolar plate is usually disposed
between adjacent battery cells. Specifically, the cell stack is
formed by stacking a bipolar plate, a positive electrode, a
membrane, a negative electrode, another bipolar plate in that order
repeatedly.
[0005] The RF battery is typically used by constructing an RF
battery system including a circulation mechanism that circulates
and supplies electrolytes to the RF battery. The circulation
mechanism includes tanks that respectively stores a positive
electrode electrolyte and a negative electrode electrolyte, pipes
that connect each of the tanks to the RF battery, and pumps
provided on the pipes. In PTL 1 and PTL 2, a bipolar plate having a
plurality of groove sections through which an electrolyte flows is
used in order to adjust a flow of the electrolyte in each cell, the
electrolyte being allowed to flow through an electrode by a pump.
Since the bipolar plate has the groove sections on a surface on the
electrode side, the flow of the electrolyte flowing through the
electrode is adjusted, thereby decreasing a pressure loss of the
electrolyte. In addition, since the bipolar plate has the groove
sections on a surface on the electrode side, the electrolyte flows
so as to traverse between the adjacent groove sections over a
section (hereinafter referred to as a "ridge section") located
between the groove sections, and the electrolyte conducts a battery
reaction on the electrode facing the ridge section to decrease the
amount of electrolyte discharged in an unreacted state.
CITATION LIST
Patent Literature
[0006] PTL 1: Japanese Unexamined Patent Application Publication
No. 2015-122230
[0007] PTL 2: Japanese Unexamined Patent Application Publication
No. 2015-210849
SUMMARY OF INVENTION
[0008] A bipolar plate according to the present disclosure is a
bipolar plate for a battery, the bipolar plate having a surface on
which a positive electrode is to be disposed and another surface on
which a negative electrode is to be disposed,
[0009] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0010] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0011] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0012] the uneven portion includes a rough surface provided on at
least a part of a surface of the ridge section, and
[0013] the rough surface has a surface roughness of 0.1 .mu.m or
more and 10 .mu.m or less in terms of arithmetical mean roughness
Ra.
[0014] A bipolar plate according to the present disclosure is
[0015] a bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed,
[0016] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0017] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0018] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0019] the uneven portion includes a step provided so as to have a
difference in height in the direction in which the adjacent groove
sections are arranged in parallel, and
[0020] the step has a maximum difference in height of 0.1 mm or
more and 0.5 mm or less.
[0021] A bipolar plate according to the present disclosure is
[0022] a bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed,
[0023] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0024] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0025] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0026] the uneven portion includes an inclined surface that
inclines from one groove section side toward the other groove
section side of the adjacent groove sections, and
[0027] the inclined surface has a difference in height of 0.1 mm or
more and 0.5 mm or less.
[0028] A cell frame according to the present disclosure includes a
bipolar plate according to any one of the bipolar plates according
to the present disclosure and a frame body disposed on an outer
periphery of the bipolar plate.
[0029] A cell stack according to the present disclosure is obtained
by stacking the cell frame according to the present disclosure, a
positive electrode, a membrane, and a negative electrode a
plurality of times.
[0030] A redox flow battery according to the present disclosure
includes the cell stack according to the present disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIG. 1 is a schematic plan view illustrating an opposed
comb-tooth shaped flow path provided on a bipolar plate according
to Embodiment 1.
[0032] FIG. 2 is a schematic enlarged sectional view illustrating
the shapes of groove sections and ridge sections provided on a
bipolar plate according to Embodiment 1.
[0033] FIG. 3 is a schematic enlarged sectional view illustrating
the shapes of groove sections and ridge sections provided on a
bipolar plate according to Embodiment 2.
[0034] FIG. 4 is a schematic enlarged sectional view illustrating
the shapes of groove sections and ridge sections provided on a
bipolar plate according to Embodiment 3.
[0035] FIG. 5 is a schematic explanatory view of a redox flow
battery.
[0036] FIG. 6 is a schematic view illustrating a configuration of a
cell stack included in a redox flow battery.
[0037] FIG. 7 is a graph showing simulation results of the
relationship between a step and a cell resistance in a bipolar
plate of Test Example 1.
DESCRIPTION OF EMBODIMENTS
Technical Problem
[0038] In each of the bipolar plates disclosed in PTL 1 and PTL 2,
most of the outermost surface of the bipolar plate is formed by
ridge sections located between respective adjacent groove sections.
Since the surfaces of the ridge sections are each constituted by a
flat surface, there is no friction between an electrode and the
bipolar plate. Thus, during the assembly of a battery cell,
positional misalignment may occur between the electrode and the
bipolar plate.
[0039] In view of the above, an object of the present disclosure is
to provide a bipolar plate capable of easily preventing positional
misalignment of an electrode during the assembly of a battery cell.
Another object of the present disclosure is to provide a bipolar
plate having good diffusibility of an electrolyte. Still another
object of the present disclosure is to provide a cell frame
including the bipolar plate, a cell stack including the cell frame,
and a redox flow battery including the cell stack.
Advantageous Effects of the Present Disclosure
[0040] The bipolar plate can easily prevent positional misalignment
of an electrode during the assembly of a battery cell. In addition,
the bipolar plate has good diffusibility of an electrolyte. The
cell frame, the cell stack, and the redox flow battery can prevent
positional misalignment of an electrode during the assembly of a
battery cell and have good diffusibility of an electrolyte.
DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION
[0041] First, the contents of embodiments of the present invention
will be listed and described.
[0042] (1) A bipolar plate according to an embodiment of the
present invention is
[0043] a bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed,
[0044] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0045] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0046] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0047] the uneven portion includes a rough surface provided on at
least a part of a surface of the ridge section, and
[0048] the rough surface has a surface roughness of 0.1 .mu.m or
more and 10 .mu.m or less in terms of arithmetical mean roughness
Ra.
[0049] Since the bipolar plate includes the uneven portion on the
ridge section that comes in contact with a positive electrode or a
negative electrode, friction is generated between the electrode and
the bipolar plate by the uneven portion, and sliding of the
electrode can be suppressed by the friction. Accordingly, the
electrode can be held on the bipolar plate by simply disposing the
electrode on a surface of the bipolar plate. Thus, even during
assembly of a battery cell, it is possible to easily prevent
positional misalignment from occurring between the electrode and
the bipolar plate.
[0050] In addition, since the bipolar plate includes the uneven
portion on the ridge section that comes in contact with a positive
electrode or a negative electrode, the uneven portion changes the
flow velocity of an electrolyte and easily generates a turbulent
flow when the electrolyte flows so as to traverse between the
adjacent groove sections. When a turbulent flow is generated in the
ridge section, the electrolyte is forcibly diffused into the
electrode disposed so as to face the ridge section, active material
ions contained in the electrolyte can be uniformly supplied into
the electrode, and thus battery reactivity can be presumably
improved.
[0051] Since the uneven portion includes the rough surface,
friction is easily generated between the electrode and the bipolar
plate, and positional misalignment of the electrode with respect to
the bipolar plate is easily prevented. Since the rough surface has
a surface roughness of 0.1 .mu.m or more in terms of arithmetical
mean roughness Ra, positional misalignment of the electrode with
respect to the bipolar plate can be prevented. On the other hand,
since the rough surface has a surface roughness of 10 .mu.m or less
in terms of arithmetical mean roughness Ra, it is easy to arrange
the electrode without a gap with respect to the bipolar plate. This
is because if a gap is formed between the bipolar plate and the
electrode, the electrolyte that flows so as to traverse between the
adjacent groove sections over the ridge section is difficult to
diffuse into the electrode, and the electrolyte may remain in an
unreacted state.
[0052] (2) A bipolar plate according to an embodiment of the
present invention is
[0053] a bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed,
[0054] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0055] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0056] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0057] the uneven portion includes a step provided so as to have a
difference in height in the direction in which the adjacent groove
sections are arranged in parallel, and
[0058] the step has a maximum difference in height of 0.1 mm or
more and 0.5 mm or less.
[0059] Since the uneven portion includes the step, a ridge line
portion extending from a high portion to a low portion can catch
the electrode, and thus positional misalignment of the electrode
with respect to the bipolar plate is easily prevented. Since the
uneven portions includes the step, when an electrolyte flows so as
to traverse between the adjacent groove sections, the flow velocity
of the electrolyte is easily significantly changed by the step-like
difference in height, and diffusibility of the electrolyte is
easily improved. Since the maximum difference in height of the step
is 0.1 mm or more, positional misalignment of the electrode with
respect to the bipolar plate can be prevented, and diffusibility of
the electrolyte is easily improved. On the other hand, since the
maximum difference in height of the step is 0.5 mm or less, the
electrode is easily arranged without a gap with respect to the
bipolar plate.
[0060] (3) A bipolar plate according to an embodiment of the
present invention is
[0061] a bipolar plate for a battery, the bipolar plate having a
surface on which a positive electrode is to be disposed and another
surface on which a negative electrode is to be disposed,
[0062] in which at least one of the surfaces of the bipolar plate
is provided with a plurality of groove sections through which an
electrolyte flows and a ridge section located between the groove
sections that are adjacent to each other,
[0063] the groove sections include an introduction groove section
and a discharge groove section that are not in communication with
each other,
[0064] the ridge section includes an uneven portion configured to
suppress sliding of the positive electrode or the negative
electrode in a direction in which the adjacent groove sections are
arranged in parallel,
[0065] the uneven portion includes an inclined surface that
inclines from one groove section side toward the other groove
section side of the adjacent groove sections, and
[0066] the inclined surface has a difference in height of 0.1 mm or
more and 0.5 mm or less.
[0067] Since the uneven portion includes the inclined surface, an
edge of the inclined surface on the high portion side can catch the
electrode, and thus positional misalignment of the electrode with
respect to the bipolar plate is easily prevented. In addition,
since the uneven portion includes the inclined surface, when an
electrolyte flows so as to traverse between the adjacent groove
sections, the flow velocity of the electrolyte is easily
significantly changed by the difference in height of the inclined
surface, and diffusibility of the electrolyte is easily improved.
Since the difference in height of the inclined surface is 0.1 mm or
more, positional misalignment of the electrode with respect to the
bipolar plate can be prevented, and diffusibility of the
electrolyte is easily improved. On the other hand, since the
difference in height of the inclined surface is 0.5 mm or less, it
is easy to arrange the electrode without a gap with respect to the
bipolar plate.
[0068] (4) An example of the bipolar plate may be
[0069] an embodiment in which the introduction groove section and
the discharge groove section satisfy any one of (A) to (C)
below:
[0070] (A) the introduction groove section and the discharge groove
section each include a comb-tooth-shaped region to form an
interdigitated, opposed comb-tooth shape in which the comb teeth
are disposed to face each other in an interdigitated manner;
[0071] (B) the introduction groove section and the discharge groove
section each include a comb-tooth-shaped region to form a
non-interdigitated, opposed comb-tooth shape in which the comb
teeth are not interdigitated with each other; and
[0072] (C) at least one of the introduction groove section and the
discharge groove section is formed by a plurality of discontinuous
groove sections.
[0073] Regarding the embodiment of (A) above, the term "comb-tooth
shape" refers to a shape that includes a long main groove extending
in one direction and a plurality of branch grooves branched from
the main groove in parallel in the same direction. The expression
"the introduction groove section and the discharge groove section
that are not in communication with each other each include a
comb-tooth-shaped region" means that in each of the introduction
groove section and the discharge groove section, branch grooves
(comb teeth) that are independent from each other protrude from an
independent main groove. Furthermore, the expression "comb teeth
are disposed to face each other in an interdigitated manner" means
that comb teeth of the introduction groove section and comb teeth
of the discharge groove section are alternately arranged with each
other in plan view.
[0074] When the comb teeth of the introduction groove section and
the discharge groove section are disposed to face each other in an
interdigitated manner, the comb teeth of the introduction groove
section and the comb teeth of the discharge groove section are
arranged in parallel, and a battery reaction in the electrode is
conducted so that an electrolyte traverses between the comb teeth
that are arranged in parallel. The amount of electrolyte flowing
through a battery reaction zone extending so as to traverse between
the comb teeth easily increases compared with the case where the
introduction groove section and the discharge groove section are
not interdigitated. Therefore, according to the above
configuration, activation of the battery reaction in the battery
reaction zone of the electrode can be expected, the flowing state
of the electrolyte in the battery reaction zone of the electrode
becomes easily uniform over the entire electrode, and the battery
reaction is easily uniformly conducted over a wide range of the
electrode.
[0075] Regarding the embodiment of (B) above, even in the case of
the non-interdigitated, opposed comb-tooth shape, a region that is
disposed to face a ridge section located between adjacent groove
sections functions as battery a reaction zone. Accordingly,
activation of the battery reaction can be expected compared with
the case where the introduction groove section and the discharge
groove section communicate with each other.
[0076] Regarding the embodiment of (C) above, the term "a plurality
of discontinuous groove sections" means that the introduction
groove section and/or the discharge groove section is formed by a
plurality of groove groups disposed at intervals in the
longitudinal direction thereof. Also in this case, a region that is
disposed to face a ridge section located between adjacent groove
sections functions as battery a reaction zone. Accordingly,
activation of the battery reaction can be expected compared with
the case where the introduction groove section and the discharge
groove section communicate with each other.
[0077] (5) A cell frame according to an embodiment of the present
invention includes the bipolar plate according to any one of (1) to
(4) above and a frame body disposed on an outer periphery of the
bipolar plate.
[0078] Since the cell frame includes the bipolar plate according to
an embodiment of the present invention, even during assembly of a
battery cell, occurrence of positional misalignment between the
electrode and the bipolar plate can be easily prevented. In
addition, the electrolyte can be forcibly diffused into the
electrode disposed so as to face the ridge section, and thus
battery reactivity can be presumably improved.
[0079] (6) A cell stack according to an embodiment of the present
invention is obtained by stacking the cell frame according to (5)
above, a positive electrode, a membrane, and a negative electrode a
plurality of times.
[0080] Since the cell stack includes the cell frame according to an
embodiment of the present invention, even during assembly of a
battery cell (cell stack), occurrence of positional misalignment
between the electrode and the bipolar plate can be easily
prevented. In addition, the electrolyte can be forcibly diffused
into the electrode disposed so as to face the ridge section, and
thus battery reactivity can be presumably improved.
[0081] (7) A redox flow battery according to an embodiment of the
present invention includes the cell stack according to (6)
above.
[0082] Since the redox flow battery includes the cell stack
according to an embodiment of the present invention, even during
assembly of a battery cell (cell stack), occurrence of positional
misalignment between the electrode and the bipolar plate can be
easily prevented. In addition, the electrolyte can be forcibly
diffused into the electrode disposed so as to face the ridge
section, and thus battery reactivity can be presumably
improved.
DETAILS OF EMBODIMENTS OF THE PRESENT INVENTION
[0083] A bipolar plate included in a redox flow battery (RF
battery) according to an embodiment of the present invention and an
RF battery including the bipolar plate will now be described in
detail with reference to the drawings. In the drawings, the same
reference signs denote the same components.
[0084] First, a basic configuration of an RF battery system
including an RF battery 100 according to an embodiment will be
described with reference to FIGS. 5 and 6. Next, embodiments of a
bipolar plate included in the RF battery 100 of the embodiment will
be described with reference to FIGS. 1 to 4.
[0085] [Overview of RF Battery]
[0086] The RF battery 100 according to the embodiment is used by
constructing an RF battery system including a circulation mechanism
that circulates and supplies electrolytes to the RF battery 100, as
illustrated in FIG. 5. The RF battery 100 is typically connected,
through an alternating current/direct current converter, a
transformer facility, and the like, to a power generation unit and
a load such as a power system or a consumer. The RF battery 100
performs charging using the power generation unit as a power supply
and performs discharging to the load as a power consumption target.
Examples of the power generation unit include solar power
generation apparatuses, wind power generation apparatuses, and
other general power plants.
[0087] [Basic Configuration of RF Battery]
[0088] The RF battery 100 includes a battery cell 100C that is
divided into a positive electrode cell 102 and a negative electrode
cell 103 by a membrane 101. The positive electrode cell 102
includes therein a positive electrode 104 to which a positive
electrode electrolyte is supplied. The negative electrode cell 103
includes therein a negative electrode 105 to which a negative
electrode electrolyte is supplied. Typically, the RF battery 100
includes a plurality of the battery cells 100C and bipolar plates
121 (FIG. 6) disposed between the respective adjacent battery cells
100C.
[0089] Each of the positive electrode 104 and the negative
electrode 105 is a reaction site in which active material ions
contained in a supplied electrolyte conduct a battery reaction. The
membrane 101 is a separation member that separates the positive
electrode 104 and the negative electrode 105 from each other and
that allows specific ions to permeate therethrough. The bipolar
plate 121 is a conductive member that is disposed between the
positive electrode 104 and the negative electrode 105 and that
allows an electric current to flow but does not allow electrolytes
to flow therethrough. Typically, as illustrated in FIG. 6, the
bipolar plate 121 is used in a state of a cell frame 120 that
includes a frame body 122 provided on the outer periphery of the
bipolar plate 121. The frame body 122 has liquid supply holes 123
and 124 through which electrolytes are supplied to the electrodes
104 and 105 disposed on the bipolar plate 121 and liquid drainage
holes 125 and 126 through which the electrolytes are discharged
from the electrodes 104 and 105, the liquid supply holes 123 and
124 and the liquid drainage holes 125 and 126 being opened on front
and back surfaces of the frame body 122. A sealing member 127 such
as an O-ring is disposed on the frame body 122 so as to surround
the entire circumference of the frame body 122.
[0090] The plurality of battery cells 100C are stacked and used in
the form of a cell stack 200. As illustrated in FIG. 6, the cell
stack 200 is formed by stacking a bipolar plate 121 of a cell frame
120, a positive electrode 104, a membrane 101, a negative electrode
105, and a bipolar plate 121 of another cell frame 120 in that
order repeatedly. On the electrodes 104 and 105 located on both
ends of the cell stack 200 in a direction in which the battery
cells 100C are stacked, current collector plates (not illustrated)
are disposed instead of the bipolar plates 121. On both ends of the
cell stack 200 in the direction in which the battery cells 100C are
stacked, end plates 201 are typically disposed. The battery cells
100C between the pair of end plates 201 are integrated by being
connected together by using connecting members 202 such as long
bolts.
[0091] [Overview of RF Battery System]
[0092] The RF battery system includes an RF battery 100, and a
positive electrode circulation mechanism and a negative electrode
circulation mechanism described below. The RF battery system
circulates and supplies the positive electrode electrolyte to the
positive electrode 104 and circulates and supplies the negative
electrode electrolyte to the negative electrode 105. FIG. 5
illustrates an operating principle of a vanadium-based RF battery
100 that uses a vanadium electrolyte containing vanadium (V) ions
as active materials of the positive electrode electrolyte and the
negative electrode electrolyte. Through the circulation and supply,
the RF battery 100 conducts charging and discharging accompanying a
valence change reaction of an ion serving as the active material in
the electrolyte for each electrode. In the battery cell 100C in
FIG. 5, the solid-line arrows indicate a charging reaction, and the
broken-line arrows indicate a discharging reaction.
[0093] The positive electrode circulation mechanism includes a
positive electrode tank 106 that stores a positive electrode
electrolyte to be supplied to the positive electrode 104, pipes 108
and 110 that connect the positive electrode tank 106 and the RF
battery 100, and a pump 112 provided on the pipe 108 on the supply
side. Similarly, the negative electrode circulation mechanism
includes a negative electrode tank 107 that stores a negative
electrode electrolyte to be supplied to the negative electrode 105,
pipes 109 and 111 that connect the negative electrode tank 107 and
the RF battery 100, and a pump 113 provided on the pipe 109 on the
supply side. By stacking a plurality of cell frames 120, the liquid
supply holes 123 and 124 and the liquid drainage holes 125 and 126
(FIG. 6) form electrolyte flow ducts, and the pipes 108 to 111 are
connected to the ducts. The basic configuration of the RF battery
system may be obtained by appropriately using a known
configuration.
[0094] [Main Feature of RF Battery]
[0095] The RF battery 100 of the embodiment includes a bipolar
plate including a plurality of groove sections through which an
electrolyte flows and a ridge section located between the adjacent
groove sections, the groove sections and the ridge section being
disposed on at least one of a surface facing the positive electrode
104 and a surface facing the negative electrode 105. A feature of
this bipolar plate lies in that the bipolar plate has a
configuration in which when the positive electrode 104 or the
negative electrode 105 is disposed on the bipolar plate, positional
misalignment of the electrode 104 or 105 with respect to the
bipolar plate can be prevented. Specifically, the ridge section
includes an uneven portion configured to suppress sliding of the
positive electrode 104 or the negative electrode 105 in a direction
in which the adjacent groove sections are arranged in parallel.
Bipolar plates included in the RF battery 100 according to the
above-described embodiment will now be described in detail. For the
sake of convenience of explanation, each of the bipolar plates
illustrated in FIGS. 2 to 4 has a larger thickness than the
positive electrode 104 and the negative electrode 105.
Embodiment 1
[0096] A bipolar plate 1 according to Embodiment 1 will be
described with reference to FIGS. 1 and 2. The bipolar plate 1 is a
rectangular flat plate as illustrated in FIG. 1. On front and back
surfaces of the bipolar plate 1, a positive electrode 104 and a
negative electrode 105 of adjacent battery cells 100C are disposed.
The bipolar plate 1 includes, on surfaces facing the electrodes 104
and 105, a plurality of groove sections 10 and ridge sections 20
located between the respective adjacent groove sections 10. The
plurality of groove sections 10 function as a flow path in which an
electrolyte flows and are provided in order to adjust flows of
electrolytes in each of the battery cells 100C, the electrolytes
being allowed to flow through the electrodes 104 and 105 by the
pumps 112 and 113, respectively. A positive electrode electrolyte
is allowed to flow in the groove sections 10 provided on one
surface of the bipolar plate 1 on which the positive electrode 104
is disposed to face the bipolar plate 1. A negative electrode
electrolyte is allowed to flow in the groove sections 10 provided
on the other surface of the bipolar plate 1 on which the negative
electrode 105 is disposed to face the bipolar plate 1. The flow of
the electrolyte in each of the battery cell 100C can be controlled
by adjusting, for example, the shape and dimensions of the groove
sections 10.
[0097] Groove Section
[0098] As illustrated in FIG. 1, the groove sections 10 include an
introduction groove section 12 through which an electrolyte is
introduced into a corresponding electrode and a discharge groove
section 14 through which the electrolyte is discharged from the
corresponding electrode. The introduction groove section 12 and the
discharge groove section 14 are not in communication with each
other but are independent from each other. The introduction groove
section 12 and the discharge groove section 14 each include a
comb-tooth-shaped region. This embodiment provides an
interdigitated, opposed comb-tooth shape in which comb teeth of the
introduction groove section 12 and comb teeth of the discharge
groove section 14 are disposed to face each other in an
interdigitated manner.
[0099] The introduction groove section 12 includes an introduction
port 12i through which is connected to the liquid supply hole 123
(or 124, FIG. 6) and through which an electrolyte is supplied, a
single introduction longitudinal groove section 12y connected to
the introduction port 12i and extending in the longitudinal
direction of the bipolar plate 1 (in the up-down direction in FIG.
1), and a plurality of introduction lateral groove sections 12x
extending from the introduction longitudinal groove section 12y in
the lateral direction of the bipolar plate 1 (in the left-right
direction in FIG. 1) and arranged in parallel with a predetermined
distance W (FIG. 1). The introduction port 12i, the introduction
longitudinal groove section 12y, and the introduction lateral
groove sections 12x are continuous.
[0100] The discharge groove section 14 has a shape similar to the
introduction groove section 12. The discharge groove section 14
includes a discharge port 14o through which is connected to the
liquid drainage hole 125 (or 126, FIG. 6) and through which the
electrolyte flowing from the introduction groove section 12 through
the electrode 104 or 105 is discharged, a single discharge
longitudinal groove section 14y connected to the discharge port 14o
and extending in the longitudinal direction of the bipolar plate 1,
and a plurality of discharge lateral groove sections 14x extending
from the discharge longitudinal groove section 14y in the lateral
direction of the bipolar plate 1 and arranged in parallel with a
predetermined distance W. The discharge port 14o, the discharge
longitudinal groove section 14y, and the discharge lateral groove
sections 14x are continuous.
[0101] In this embodiment, as illustrated in FIG. 2, each of the
groove sections 10 has a rectangular sectional shape. The sectional
shape of the groove section 10 may be a V-shape, a U-shape, a
semicircular shape, or the like besides a rectangular shape. In
this embodiment, in the case where the groove sections 10 are
provided on the front and back surfaces of the bipolar plate 1, the
bipolar plate 1 includes the lateral groove sections 12x and 14x at
different positions in perspective plan view. The groove sections
10 may be provided such that the lateral groove sections 12x and
14x are located at positions that partially overlap or at positions
that do not overlap in perspective plan view of the bipolar plate
1.
[0102] Ridge Section
[0103] As illustrated in FIGS. 1 and 2, the ridge sections 20 are
sections located between adjacent groove sections 10. In this
embodiment, the groove sections 10 form an interdigitated, opposed
comb-tooth shape in which comb teeth of the introduction groove
section 12 and comb teeth of the discharge groove section 14 are
disposed to face each other in an interdigitated manner.
Accordingly, the term "ridge section 20" refers to a section
located between the introduction lateral groove section 12x and the
discharge lateral groove section 14x (refer to FIG. 2). The ridge
sections 20 form most of the outermost surface of the bipolar plate
1. Therefore, when the battery cell 100C is assembled, the ridge
sections 20 contact the electrodes 104 and 105.
[0104] As illustrated in FIG. 2, each of the ridge sections 20 has
an uneven portion 22 configured to suppress sliding of the
electrode 104 or 105 in a direction in which an introduction
lateral groove section 12x and a discharge lateral groove section
14x that are adjacent to each other are arranged in parallel. A
feature of this embodiment lies in that the uneven portion 22 is
formed by a rough surface provided on a surface of the ridge
section 20.
[0105] The rough surface forming the uneven portion 22 has a
surface roughness of 0.1 .mu.m or more and 10 .mu.m or less in
terms of arithmetical mean roughness Ra. In general, the positive
electrode 104 and the negative electrode 105 are each formed of a
porous body including fibers. When the surface roughness of the
rough surface is 0.1 .mu.m or more in terms of arithmetical mean
roughness Ra, the ridge sections 20 can catch the fibers that form
the electrodes 104 and 105. Thus, positional misalignment of the
electrodes 104 and 105 with respect to the bipolar plate 1 can be
prevented. On the other hand, when the surface roughness of the
rough surface is 10 .mu.m or less in terms of arithmetical mean
roughness Ra, it is easy to arrange the electrodes 104 and 105
without gaps with respect to the bipolar plate 1. This is because
if a gap is formed between the bipolar plate 1 and the electrode
104 or 105, an electrolyte that flows so as to traverse between
adjacent groove sections 12x and 14x over a ridge section 20 is
difficult to diffuse into the electrode 104 or 105, and the
electrolyte may remain in an unreacted state. The surface roughness
of the rough surface is more preferably 6.4 .mu.m or less, 3.2
.mu.m or less, and particularly preferably 0.2 .mu.m or more and
1.6 .mu.m or less in terms of arithmetical mean roughness Ra.
[0106] In the bipolar plate 1, each of the electrolytes introduced
from the introduction port 12i flows along the groove sections 10
(in the directions indicated by the solid-line arrows in FIG. 1)
and flows to traverse in a width direction (in the up-down
direction in FIG. 1) over each ridge section 20 between the
corresponding introduction lateral groove section 12x and discharge
lateral groove section 14x (in the directions indicated by the
broken-line arrows in FIG. 1). The electrolytes flowing through the
groove sections 10 during the time in which the electrolytes are
introduced from the introduction ports 12i and reach the discharge
ports 14o permeate and diffuse into the electrodes 104 and 105
disposed so as to face the bipolar plate 1. The electrolytes that
permeate and diffuse into the electrodes 104 and 105 conduct
battery reactions in the electrodes 104 and 105. In this
embodiment, since each of the electrolytes flows so as to traverse
over the ridge sections 20, the amount of electrolyte that is
discharged in an unreacted state can be decreased. In particular,
since the ridge sections 20 include uneven portions 22, the flow
velocities of electrolytes are changed by a minute difference in
height of the uneven portions 22, and thus turbulent flows of the
electrolytes can be presumably generated. When turbulent flows are
generated in the ridge sections 20, the electrolytes are forcibly
diffused into the electrodes 104 and 105 disposed so as to face the
ridge sections 20, active material ions contained in the
electrolytes can be uniformly supplied into the electrodes 104 and
105, and thus battery reactivity can be presumably improved.
[0107] With an increase in a length L (FIG. 1) of the portion where
the comb teeth of the introduction groove section 12 and the comb
teeth of the discharge groove section 14 are interdigitated with
each other, the amount of electrolyte that flows so as to traverse
over the ridge sections 20 presumably increases. Accordingly, the
length of the interdigitated portion may be 80% or more, and
furthermore, 90% or more of the length of the bipolar plate 1 (the
length in the left-right direction in FIG. 1).
[0108] In addition, with an increase in the distance W between the
introduction groove section 12 and the discharge groove section 14,
that is, a width W of each of the ridge sections 20, the amount of
electrolyte that flows so as to traverse over the ridge sections 20
presumably increases. Accordingly, the length of the width W of
each of the ridge sections 20 may be 100% or more and 700% or less,
and furthermore, 200% or more and 500% or less of the width of each
of the groove sections 10.
[0109] In this embodiment, the uneven portion 22 is provided over
the entire width W of the corresponding ridge section 20.
Alternatively, the uneven portion 22 may be partially provided on
the ridge section 20 in the width direction.
[0110] A conductive material with a low electrical resistance that
does not react with an electrolyte and has electrolyte resistance
(such as chemical resistance and acid resistance) can be suitably
used as the constituent material of the bipolar plate 1.
Furthermore, the constituent material of the bipolar plate 1
preferably has suitable rigidity. This is because the shape and the
dimensions of the groove sections 10 are unlikely to change for a
long period of time, and it is easy to maintain the effect reducing
flow resistance and the effect of reducing a pressure loss that are
achieved by the groove sections 10. Specific examples of the
constituent material include a composite material containing a
carbon material and an organic material. More specifically,
examples thereof include conductive plastics containing a
conductive inorganic material, such as graphite, and an organic
material, such as a polyolefin-based organic compound or a
chlorinated organic compound.
[0111] Examples of the carbon material include, in addition to
graphite, carbon black and diamond like carbon (DLC). Examples of
carbon black include acetylene black and furnace black. The carbon
material preferably contains graphite. The carbon material may
contain mainly graphite and partly at least one of carbon black and
DLC. The conductive inorganic material may contain, in addition to
the carbon material, a metal such as aluminum. Examples of the
conductive inorganic material include powders and fibers.
[0112] Examples of the polyolefin-based organic compound include
polyethylene, polypropylene, and polybutene. Examples of the
chlorinated organic compound include vinyl chloride, chlorinated
polyethylene, and chlorinated paraffin.
[0113] The bipolar plate 1 described above can be produced by
forming the above constituent material to have a plate shape by a
known method, such as injection molding, press molding, or vacuum
molding, and forming, in addition to the groove sections 10 and the
ridge sections 20, the uneven portions 22 on the ridge sections 20.
When the groove sections 10 and the uneven portions 22 are
simultaneously formed, good productivity of the bipolar plate 1 can
be achieved. Alternatively, the groove sections 10 and the uneven
portions 22 may be formed by, for example, cutting a flat plate
that is not provided with the groove sections 10. The rough surface
may be formed on the ridge sections 20 by subjecting the ridge
sections 20 to blasting.
Embodiment 2
[0114] A bipolar plate 2 according to Embodiment 2 will be
described with reference to FIG. 3. A feature of the bipolar plate
2 lies in that uneven portions 22 included in ridge sections 20 are
each formed by a step. The bipolar plate 2 of Embodiment 2 differs
from the bipolar plate 1 of Embodiment 1 in the form of the uneven
portions 22, and other configurations of the bipolar plate 2 of
Embodiment 2 are the same as those of the bipolar plate 1 of
Embodiment 1. FIG. 3 illustrates only one surface side of the
bipolar plate 2.
[0115] As illustrated in FIG. 3, a step H that forms an uneven
portion 22 has a difference in height in a direction in which an
introduction lateral groove section 12x and a discharge lateral
groove section 14x that are adjacent to each other are arranged in
parallel. In this embodiment, a single step is provided such that
the thickness of the bipolar plate 2 decreases from the
introduction lateral groove section 12x side toward the discharge
lateral groove section 14x side. In this embodiment, the
introduction lateral groove section 12x side is referred to as a
"high portion 22h", and the discharge lateral groove section 14x
side is referred to as a "low portion 22p".
[0116] The step H that forms each of the uneven portions 22 has a
maximum difference in height of 0.1 mm or more and 0.5 mm or less.
When the maximum difference in height of the step is 0.1 mm or
more, ridge line portions formed by the high portions 22h and the
low portions 22p can catch the electrodes 104 and 105, and thus
positional misalignment of the electrodes 104 and 105 with respect
to the bipolar plate 2 can be prevented. When the maximum
difference in height of the step is 0.1 mm or more, the flow
velocity of an electrolyte that flows from the introduction lateral
groove section 12x side to the discharge lateral groove section 14x
side through the ridge section 20 significantly changes, and a
turbulent flow of the electrolyte is easily generated. The reason
for this is as follows. When the battery cell 100C is assembled and
compressed, as illustrated in FIG. 3, the distance between the
bipolar plate 2 and the membrane 101 on the low portion 22p side is
larger than that on the high portion 22h side, and thus the flow
velocity on the low portion 22p side becomes lower than that on the
high portion 22h side. On the other hand, when the maximum
difference in height of the step is 0.5 mm or less, each of the
electrodes 104 and 105 is easily arranged without a gap with
respect to the bipolar plate 2. The maximum difference in height is
more preferably 0.2 mm or more and 0.4 mm or less.
[0117] In this embodiment, a single step is provided in a central
portion of each of the ridge sections 20 in the width direction.
Alternatively, a plurality of steps may be provided. In this
embodiment, the introduction lateral groove section 12x side forms
the high portion 22h, and the discharge lateral groove section 14x
side forms the low portion 22p. Alternatively, the introduction
lateral groove section 12x side may form the low portion 22p, and
the discharge lateral groove section 14x side may form the high
portion 22h. In the case where a plurality of steps are provided on
a single ridge section 20, it is not necessary that the height
sequentially decrease or increase from one side toward the other
side of the ridge section 20 in the width direction. For example,
both sides in the width direction may form high portions 22h (low
portions 22p) and a central portion may form a low portion 22p
(high portion 22h). Alternatively, high portions 22h and low
portions 22p may be irregularly provided.
[0118] Each of the ridge sections 20 of the bipolar plate 2 may
have a smooth surface having a surface roughness of less than 1.0
.mu.m in terms of arithmetical mean roughness Ra or a rough surface
having a surface roughness of 1.0 .mu.m or more in terms of Ra.
Embodiment 3
[0119] A bipolar plate 3 according to Embodiment 3 will be
described with reference to FIG. 4. A feature of the bipolar plate
3 lies in that uneven portions 22 included in ridge sections 20 are
each formed by an inclined surface. The bipolar plate 3 of
Embodiment 3 differs from the bipolar plate 1 of Embodiment 1 in
the form of the uneven portions 22, and other configurations of the
bipolar plate 3 of Embodiment 3 are the same as those of the
bipolar plate 1 of Embodiment 1. FIG. 4 illustrates only one
surface side of the bipolar plate 3.
[0120] As illustrated in FIG. 4, the inclined surface that forms an
uneven portion 22 inclines from the introduction lateral groove
section 12x side toward the discharge lateral groove section 14x
side of an introduction lateral groove section 12x and a discharge
lateral groove section 14x that are adjacent to each other. In this
embodiment, the inclined surface inclines such that the thickness
of the bipolar plate 3 decreases from the introduction lateral
groove section 12x side toward the discharge lateral groove section
14x side. In this embodiment, the introduction lateral groove
section 12x side is referred to as a "high portion 22h", and the
discharge lateral groove section 14x side is referred to as a "low
portion 22p".
[0121] The inclined surface that forms each of the uneven portions
22 has a difference in height of 0.1 mm or more and 0.5 mm or less.
When the difference in height of the inclined surface is 0.1 mm or
more, the electrodes 104 and 105 can be caught on the high portion
22h side, and thus positional misalignment of the electrodes 104
and 105 with respect to the bipolar plate 3 can be prevented. When
the difference in height of the inclined surface is 0.1 mm or more,
the flow velocity of an electrolyte that flows from the
introduction lateral groove section 12x side to the discharge
lateral groove section 14x side through the ridge section 20
significantly changes, and a turbulent flow of the electrolyte is
easily generated. The reason for this is as follows. When the
battery cell 100C is assembled and compressed, as illustrated in
FIG. 4, the distance between the bipolar plate 3 and the membrane
101 on the low portion 22p side is larger than that on the high
portion 22h side, and thus the flow velocity on the low portion 22p
side becomes lower than that on the high portion 22h side. On the
other hand, when the difference in height of the inclined surface
is 0.5 mm, each of the electrodes 104 and 105 is easily arranged
without a gap with respect to the bipolar plate 3. The difference
in height of the inclined surface is more preferably 0.2 mm or more
and 0.4 mm or less.
[0122] In this embodiment, the inclined surface continuously
inclines from a side edge of the introduction lateral groove
section 12x to a side edge of the discharge lateral groove section
14x. Alternatively, in addition to an inclined surface, a flat
surface or a step may be provided between the two side edges. In
this embodiment, the introduction lateral groove section 12x side
forms the high portion 22h, and the discharge lateral groove
section 14x side forms the low portion 22p. Alternatively, the
introduction lateral groove section 12x side may form the low
portion 22p, and the discharge lateral groove section 14x side may
form the high portion 22h.
[0123] Each of the ridge sections 20 of the bipolar plate 3 may
have a smooth surface having a surface roughness of less than 1.0
.mu.m in terms of arithmetical mean roughness Ra or a rough surface
having a surface roughness of 1.0 .mu.m or more in terms of Ra.
Modifications
[0124] The bipolar plates 1 to 3 of Embodiments 1 to 3 may have any
of the following arrangement forms of the groove sections 10.
[0125] (1) In the case of the interdigitated, opposed comb-tooth
shape, comb teeth of the introduction groove section 12 and comb
teeth of the discharge groove section 14 extend in the longitudinal
direction (in the up-down direction in FIG. 1) and are alternately
arranged in the lateral direction of the bipolar plate (in the
left-right direction in FIG. 1).
[0126] (2) The groove sections 10 form a non-interdigitated,
opposed comb-tooth shape in which the introduction groove section
12 and the discharge groove section 14 are not interdigitated with
each other. For example, the groove sections 10 may have a form in
which an introduction groove section and a discharge groove section
are disposed to face each other with a distance therebetween in the
lateral direction of the bipolar plate. Also in such a
non-interdigitated comb-tooth shape, in each of the electrode 104
and 105, regions that are disposed to face the ridge sections
located between adjacent groove sections each function as a battery
reaction zone.
[0127] (3) At least one of the introduction groove section 12 and
the discharge groove section 14 is formed not by a continuous
groove section but by a plurality of discontinuous groove sections.
For example, an introduction lateral groove section and/or a
discharge lateral groove section may be formed by a plurality of
groove groups disposed at intervals in the lateral direction
thereof.
[0128] [Other Constitutional Members of RF Battery]
[0129] Positive Electrode and Negative Electrode
[0130] The positive electrode 104 and the negative electrode 105
are each disposed between the membrane 101 and the bipolar plate 1,
2, or 3. An electrolyte is supplied to each of the electrodes 104
and 105 mainly through the groove sections 10 of the bipolar plate
1, 2, or 3. The electrolyte permeates and diffuses into the
corresponding electrode 104 or 105, and an active material in the
electrolyte conducts a battery reaction on the corresponding
electrode 104 or 105. For this purpose, each of the electrodes 104
and 105 is formed of a porous body having a large number of fine
pores. As the constituent material of each of the electrodes 104
and 105, a porous body containing carbon fibers, for example,
carbon felt or carbon paper can be suitably used. Known electrodes
can be used.
[0131] Membrane
[0132] Examples of the membrane 101 include ion-exchange membranes
such as cation-exchange membranes and anion-exchange membranes.
Ion-exchange membranes have the features that (1) they have good
isolation properties between ions of the positive electrode active
material and ions of the negative electrode active material, and
(2) they have good permeability of H.sup.+ ions, which are charge
carriers in the battery cell 100C. Thus, ion-exchange membranes can
be suitably used as the membrane 101. Known membranes can be
used.
[0133] [Electrolyte]
[0134] The electrolyte used in the RF battery 100 contains active
material ions such as metal ions or non-metal ions. An example
thereof is a vanadium-based electrolyte containing vanadium ions
having different valences (FIG. 5) as a positive electrode active
material and a negative electrode active material. Other examples
thereof include an iron-chromium-based electrolyte containing iron
(Fe) ions as the positive electrode active material and chromium
(Cr) ions as the negative electrode active material, and a
manganese-titanium-based electrolyte containing manganese (Mn) ions
as the positive electrode active material and titanium (Ti) ions as
the negative electrode active material. For example, an aqueous
solution containing, in addition to the active materials, at least
one acid selected from sulfuric acid, phosphoric acid, nitric acid,
and hydrochloric acid or at least one salt of the acid can be used
as the electrolyte.
[0135] [Use]
[0136] The bipolar plates of the embodiments can be suitably used
as bipolar plates of redox flow batteries. The redox flow batteries
of the embodiments can be used as storage batteries for the purpose
of, for example, stabilization of output fluctuation of power
generation, storage of electricity when surplus power is generated,
and load leveling for power generation using natural energy, such
as solar power generation or wind power generation. The redox flow
batteries of the embodiments may be additionally installed in
typical power plants and used as storage batteries for the
countermeasures against voltage sag/power failure and load
leveling. In particular, the redox flow batteries of the
embodiments can be suitably used as large-capacity storage
batteries for the purposes described above.
Test Example 1
[0137] In Test Example 1, a bipolar plate which included a flow
path having an interdigitated comb-tooth shape and which was
provided with ridge sections including uneven portions formed by
steps was used (refer to FIG. 3), and a fluid simulation (numerical
analysis using spreadsheet software of Excel (registered trademark)
available from Microsoft Corporation) was conducted for an RF
battery in which the above bipolar plate was assumed to be disposed
at a predetermined position. Thus, a cell resistance of the RF
battery was determined. In Test Example 1, the RF battery had a
single-cell structure in which a battery cell including a positive
electrode-membrane-negative electrode stack was sandwiched between
cell frames each including the bipolar plate. Detailed conditions
for the test are described below.
[0138] Bipolar Plate
[0139] Dimensions: length 200 mm, width 198 mm, thickness 6.2 mm
Shape of groove section: interdigitated, opposed comb-tooth shape
including introduction groove section and discharge groove section
(refer to FIG. 3)
[0140] With regard to lateral groove sections [0141] Number: 16
introduction groove sections.times.16 discharge groove sections
[0142] Length L: 150 mm [0143] Overlap length of comb teeth: 142 mm
[0144] Width of groove section: 1.3 mm [0145] Depth of groove
section: 1.0 mm [0146] Sectional shape of groove section:
rectangular shape [0147] Width W of ridge section: 3.9 mm
[0148] With regard to longitudinal groove section [0149] Length L:
170 mm
[0150] Constituent material: bipolar plate obtained by compacting
80% by mass of graphite and 20% by mass of polypropylene as matrix
resin
[0151] Electrode
[0152] Dimensions: length 170 mm, width 150 mm, thickness 0.5 mm
[0153] Constituent material: carbon felt containing carbon fiber
and binder carbon GDL10AA available from SGL CARBON JAPAN Co.,
Ltd.
[0154] Membrane
[0155] Constituent material: Nafion (registered trademark) 212
available from E. I. du Pont de Nemours and Company
[0156] Electrolyte
[0157] Composition: aqueous V sulfate solution (V concentration:
1.7 mol/L, sulfuric acid concentration: 4.3 mol/L)
[0158] Flow rate: 300 mL/min
[0159] FIG. 7 shows a graph of a cell resistance (normalized on the
assumption that the cell resistance when a step H is 0 mm is 1)
when the step H formed on each ridge section of the bipolar plate
(uneven portion: maximum difference in height) was changed. In FIG.
7, the horizontal axis represents the step H (mm), and the vertical
axis represents the normalized cell resistance. Referring to FIG.
7, as compared with a cell resistance Rs when the step H was 0.01
mm, a ratio of decrease in a cell resistance Rx ((Rs-Rx)/Rs) was as
follows when the step H was changed. The ratio of decrease was
about 2% when the step H was 0.1 mm, the ratio of decrease was
about 4% when the step H was 0.2 mm, the ratio of decrease was
about 6% when the step H was 0.3 mm, the ratio of decrease was
about 7% when the step H was 0.4 mm, and the ratio of decrease was
about 9% when the step H was 0.5 mm. Specifically, the results show
that with an increase in the step H, the cell resistance is
decreased, and the electrolyte has good diffusibility. However, if
the step H is excessively large, a gap is formed between the
bipolar plate and the positive electrode or between the bipolar
plate and the negative electrode, it is difficult for the
electrolyte that flows so as to traverse between adjacent groove
sections over a ridge section to diffuse into the electrodes, and
the electrolyte may remain in an unreacted state. In addition, when
the step H is increased and the gap between the bipolar plate and
the positive electrode or between the bipolar plate and the
negative electrode is increased, the compression ratio decreases,
which may result in a problem of an increase in the contact
resistance between the bipolar plate and the positive electrode or
between the bipolar plate and the negative electrode. Accordingly,
the step H is preferably 0.5 mm or less.
[0160] The present invention is not limited to the examples. The
scope of the present invention is defined by the appended claims
and is intended to include all modifications within the meaning and
scope equivalent to those of the claims. For example,
specifications of the groove sections (such as the sizes, shapes,
and numbers of the lateral groove sections and the longitudinal
groove sections) of the bipolar plate, the type of electrolyte, and
the like may be changed.
REFERENCE SIGNS LIST
TABLE-US-00001 [0161] 100 redox flow battery (RF battery) 100C
battery cell 101 membrane 102 positive electrode cell 103 negative
electrode cell 104 positive electrode 105 negative electrode 106
positive electrode tank 107 negative electrode tank 108 to 111 pipe
112, 113 pump 200 cell stack 201 end plate 202 connecting member
120 cell frame 121 bipolar plate 122 frame body 123, 124 liquid
supply hole 125, 126 liquid drainage hole 127 sealing member 1, 2,
3 bipolar plate 10 groove section 12 introduction groove section
12i introduction port 12x introduction lateral groove section 12y
introduction longitudinal groove section 14 discharge groove
section 14o discharge port 14x discharge lateral groove section 14y
discharge longitudinal groove section 20 ridge section 22 uneven
portion 22h high portion 22p low portion
* * * * *